The ability to remotely sense magnetic fields without direct physical presence or contact with the field location is important in many applications. These applications include the measurement of magnetic field changes in a difficult or hostile environment (such as earthquake warning or battlefield sensing, which are usually performed by a magnetometer in close physical proximity), or the sensing of information in a magnetic storage medium (as usually performed by a flying head of a computer hard disk drive). Another important application involves contactless sensing of current pulses on a microelectronic chip, especially the submicron scale interconnect lines used to wire the various parts of a chip together, and which limit the speed of the operation of the chip. The present methods for sensing and/or measuring magnetic fields, whether on a macroscale or a microscale, make telemetry cumbersome, as the measured magnetic fields or changes therein are detected by a magnetic field sensitive ‘resistor’ that converts the magnetic field information to an electrical signal. This approach typically requires physical placement of wires to the magnetic sensor element or its immediate vicinity. “Wireless” sensing offers many advantages over the conventional wired approach, but is more difficult to implement by conventional techniques. For example, in this case the telemetry may require the incorporation of a microwave transmitter as part of the sensor package. This requirement adds cost, complexity and increased power constraints to the sensor package.
It is well known in the art that certain magneto-optic effects exist. More specifically, the Kerr effect and the Faraday effect correspond to a change in the intensity or polarization state of light either reflected from (Kerr) or transmitted through (Faraday) a magnetic material. Since the amount of change in the polarization state or intensity is proportional to the magnetisation in the material, it is possible to use these effects to examine magnetic properties of materials. However, the use of the Kerr or Faraday effects requires a light source that can be disposed to illuminate a material of interest, as well as a detector that can be disposed to receive the reflected or transmitted light. For a number of important applications these requirements can be difficult to satisfy in a cost effect and simple manner.